Aluminum-containing compound semiconductors are an integral part of many of today's high-performance electronic and optoelectronic devices, such as laser diodes (LDs) and light emitting diodes (LEDs). One ternary semiconductor compound which is frequently used in these devices comprises epitaxial layers of aluminum gallium arsenide (Al.sub.x Ga.sub.1-x As). Aluminum-containing semiconductor crystals are grown by a wide variety of known techniques, such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD).
The efficiency and performance of devices which contain aluminum-based semiconductors are adversely effected by the presence of impurities in the semiconductor crystal. Some of the more common contaminants found in these semiconductors are oxygen and germanium. For example, contamination of the growing semiconductor with as little as 1 part per million of oxygen in the vapor phase will result in concentrations of oxygen in excess of 10.sup.19 cm.sup.3 in the Al.sub.x Ga.sub.1-x As solid. These impurities are typically found in the source materials used to grow the semiconductor, as well as in the growth apparatus itself. Reducing the presence of the so-called "deep level" contaminants has proven to be a significant challenge to those attempting to produce high quality Al.sub.x Ga.sub.1-x As semiconductor crystals.
One known method for reducing the concentration of deep-level impurities in n-type or p-type AlGaAs semiconductors is to purify separately each of the component elements used to produce the alloy. In U.S. Pat. No. 2,975,048, for example, each component element of a semiconductor compound (GaAs) is purified through oxidation, isolation of the impurity oxide, and finally, reduction of the pure oxide. Such a method, however, requires expensive gettering devices, filtration systems, and/or source purification techniques, greatly adding to the cost and complexity of the crystal growth process. Moreover, the level of purity achieved by such techniques is not sufficient for many of today's advanced semiconductor applications. Nor will such techniques completely remove all oxygen and germanium impurities.
Other methods for producing high-purity semiconductor materials have been proposed. For example, U.S. Pat. No. 3,297,403 discloses a method for preparing a semiconductor compound by selectively melting the elements which make up the compound in an evacuated ampoule. This method adds to the complexity and expense of the semiconductor growth process. Moreover, the level of compound purity achieved by the method of the '403 patent is insufficient for today's high-speed LDs and LEDs.